Subject: RE: [mobile-ip] Simple Analysis of Mobile IP v4

From: "Subrata Goswami" <[email-masked]>
Date: Sun, 15 Sep 2002 12:50:02 -0700

Okay Chip, you know more about Mobile-IP and Communications systems
than me.  Let us stick to IP and 802.11 for the time being.

From you description of bicasting and simulcasting, it appears to me
that it all happens in the physical and link layer. How common are
those in 802.11 environment ? Has the IEEE defined their position in
this
regard ? If those things happen, they actually worsen the situation for
HA - don't they ? 

Actually if you do simulcasting (if it is possible to do at all), the
actual number can be higher by a factor equal to the number of
neighboring AP's, which in 802.11b is 6 - more than the x2 you
mentioned.

You have been mentioning about some physical limit - are those still
applicable if you use fiber and repeaters ?  For example, you can also
put 6
802.11a AP's side by side if you want or 3 802.11b AP's, can not you? 
That lets you use 9 AP's in the same area, right? You can now connect
these to a L2 switch , right ?

Okay, so you are saying it is no big deal to do fast lookup in a 64K
table, right ? I have not heard of Effnet, but that name has a pretty
embarrassing meaning in English.

You have mentioned some interesting numbers, " You seem to be ignoring
the interframe spacing, the headers, ... .The average service time for a
64 byte packet by a Lucent WavePOINT-II AP is 918 usec (microseconds) on
the downlink and 190usec on the uplink.". Do you have a breakdown of
these numbers?  From MN to AP, AP to Switch, Switch to whatever? What do
these
64 byte packets contain?

As for 64K MN's sharing the same RF spectrum, I would not limit myself
to what is available today. You can in fact use directional/adaptive
antennas etc. to do Spatial Division Multiplexing of radio waves.

Let me know, when I have cleared your communications tests.

Regards

Subrata

-----Original Message-----
From: Gerald Maguire [mailto:[email-masked]] 
Sent: Sunday, September 15, 2002 11:39 AM
To: [email-masked]
Subject: Re: [mobile-ip] Simple Analysis of Mobile IP v4

Please note that I am not sending this to the mailing list.

It would appear from your questions and your draft that you don't
actually understand Mobile IP and have not read very much about the
protocol. It would also appear that you have very little actual
practical knowledge of communication systems.

    1. Can you please tell me what exactly are bicasting and
simulcasting.
Bi-casting -- involves sending copies of the packet to the mobile via
two routes (the existing AP and the "new" AP) - thus it can
substantially decrease loss and provide a smooth handover even of the
two networks are of different types.

Simulcasting -- extends this to be potentially N different copies via
N different links.

    2. Why do you need to create tunnels to the MN (if the FA is not
    co-located) ?

You are going to tunnel the traffic from the home agent at least to the
FA.
In the case of the co-located FA, this means all the way to the MN.

    3. I do not see why you need more than one tunnel to communicate
with
    one MN.

See bi-casting and simulcasting above.

    4. Some situations I have described are possible, however unlikely.
If
    you have
    100 MN's in a Home Network, each of them potentially can roam into a
    different
    foreign network.

Certainly and each will get traffic forwarded to it from its home
agent. Except for periods when you are bi-casting or simulcasting -
this should result in ~2 times the total traffic as would be on the
various networks.

    5. Why do you not want to connect 25 AP's to a Ethernet port ?
    I have no comment on the economic consequence of doing so, but it is
    possible
    technically. 

You don't seem to understand that there is a limit on the length of
the cable that you can attach to the port of hub/switch/router when
using 100Tx -- which limits how far away the AP can be. {I'd suggest
you look this up in the 100Tx specification.} Then consider the
signal strength of the 802.11b AP. Knowing what the likley attenuation
is in a building at this frequency the signal will fall off as roughly
1/(r^2.5)
{note that it is 2.5 rather than 2 because it is not free space}.
In addition, you only have a small number of frequency channels for
high rate communication which don't over lap (at best 4 of them).
Now think about how many access points you can locate with the wiring
distance of 100Tx while avoiding frequency overlaps. You will see the
number is well below 25.

    6. Do you have a number for the  bandwidth consumed by AAA and
Mobile IP
    registration ?
    I am pretty sure that number is insignificant - say 2 packets of 100
    bytes per
    handoff from MN to FA. Then say 4 packets of 200 bytes from FA to
    Diameter server. 
    That is 1000 bytes per handoff - 8000 bits - takes about 80 micro
    seconds 
    (8000/100,000,000) on Fast Ethernet.   Is it easy to do a lookup in
a
    table
    of 64K entries in 80 micro seconds ?

You seem to be ignoring the interframe spacing, the headers, ... .
The average service time for a 64 byte packet by a Lucent WavePOINT-II
AP is 918 usec (microseconds) on the downlink and 190usec on the uplink.

Researchs at Luleå in Sweden have show how to do very fast lookup for
routing or filtering. This was the basis of a company Effnet:
 
http://www.effnet.com/sites/effnet/setup/eng/index.asp?section=solutions
&content=solutions_toolkit_fwdeng

As noted in my earlier message they can search backbone router sized
lookup tables at speeds sufficient to support 1Gbps ethernet
interfaces using a dual processor Pentium machine -- in _software_ not
in hardware. The above link shows their scaling to 10Gbps link speeds.

    7. Moreover the FA that terminates the tunnels has to look up the L2
    address of the
    visiting MN for every IP packet tunneled to it. So would not the
    lookup process
    be the bottleneck if you have 64K MN roam into one sub-network ?

The lookup process will not be the bottleneck, the problem will be
that the 64K nodes have to divide the limited radio spectrum!

Chip

---

From: Gerald Maguire <[email-masked]>
Date: Mon, 16 Sep 2002 14:51:24 +0200 (MET DST)

Then why are _you_ writing internet drafts?

The IEEE is concerned with the physical and link layer, while IETF is
concerned with the network layer and above. Bicasting and simulcasting
can be done by Mobile IP (since a HA sends copies of packets to all IP
addresses which are register for a given host). This functionality has
been there since the initial definition of Mobile IP. While
duplication of packets may increase traffic at times when the mobile
is about to move or when it is in a poor reception area for multiple
cells, it really reduces traffic since it increases the probability
that the packet will be delivered and the packet will not have to be
retransmitted from the source machine!

If you think about it (geometrically) there is generally little reason
to deliver the packet from more than 3 APs (in fact most of the time
only 2) since a node is either in a cell or moving toward the edge of
a cell (in which case it is moving in some direction - and packets
only need to be sent from these directions). Note also that if you are
doing simulcasting locally (i.e., invisibly to Mobile IP but using L2
information) then you can take one stream from the HA to an AP and
locally replicate this to the other APs. One of my students did a
licentiate thesis which exploited this in 1998. Note that this need
not appreciably increase the use of the wireless channels - since you
only deliver copies of packets to the APs and only send them across
the link when the MN has registered with this AP.

Fiber and repeaters are more expensive than 100Tx ports.  Yes you can
put several APs together, but you won't be able to use these
frequencies again until you are 2 * 100m away (in the case of
802.11b), i.e., in frequency re-use you can not use the same frequency
in an adjacent cell, thus you generally want to have one cell in between.

See the publications of Mikael Degermark
(http://www.cdt.luth.se/~micke/publications.html) for more information.

64 bytes of payload

Well if you are going to only consider the maximum possible case, then
why not consider entangled quantuum states, thus you have faster than
speed of light communication across arbitrary distance? Of course you
may have to wait a year or more before this will be available in Radio Shack.
Note that the look up time is no longer relevant, because you
communicate directly from the source to the destination and you don't
need any intervening network! 

As far as I know you are not enrolled and have not been enrolled in
any of my courses - so this is not a decision I have to make.

Chip

---

From: "Subrata Goswami" <[email-masked]>
Date: Mon, 16 Sep 2002 08:39:59 -0700

As for "bicasting" and "simulcasting", no one does those as far as I
know
in a practical situation. By the way, these words are not even used in
any RFC or ID, so you have to define them in an ID. You are swamping
your network with 5x more wasted packets ! Why would you like to do it
in the first place ? Does not make any sense ! 

Can you find out where your MN is, let alone its velocity and direction?
Due
to lack of that knowledge, you have to do multicasting to 6 AP's -  what
a
waste!

An AP roughly covers an area of 100m is radius, right? Sure frequency
reuse
is an issue, but if I want to have 500Mbps of bandwidth in my living
room
I can do that by running 9 AP's  side-by-side, right ? Moreover,  how
much does  a repeater cost ?  $25 ? How much does fiber cost ? $2 /
meter ? These
are not hugely expensive items.

The 64 bytes of payload of what type ? TCP ACKS , Ethernet , what ? So
the 
actual number of bytes you are sending down is probably twice that. Do
you
have any clue on where the packets are spending their time ? What you
are
stating is a very crude number, not very useful.  More research is
needed
here ! 

With all due respect to your comments on " entangled quantuum states",
what
are those ? Did you invent them?  But, Spatial Division Multiplexing
(SDM)
is here now - there are several companies that are pursuing that angle. 

Chip, are you going to pay me to not write Internet Drafts ?  Rate would
be
$1000 per ID I do not write - I will quit my job right now.

Subrata

-----Original Message-----
From: Gerald Maguire [mailto:[email-masked]] 
Sent: Monday, September 16, 2002 5:51 AM
To: [email-masked]
Cc: [email-masked]
Subject: Re: [mobile-ip] Simple Analysis of Mobile IP v4

    that it all happens in the physical and link layer. How common are
    those in 802.11 environment ? Has the IEEE defined their position in
    this
    regard ? If those things happen, they actually worsen the situation
for
    HA - don't they ? 

concerned with the network layer and aove. Bicasting and simulcasting

    Actually if you do simulcasting (if it is possible to do at all),
the
    actual number can be higher by a factor equal to the number of
    neighboring AP's, which in 802.11b is 6 - more than the x2 you
    mentioned.

    You have been mentioning about some physical limit - are those still
    applicable if you use fiber and repeaters ?  For example, you can
also
    put 6
    802.11a AP's side by side if you want or 3 802.11b AP's, can not
you? 
    That lets you use 9 AP's in the same area, right? You can now
connect
    these to a L2 switch , right ?

in an adjacent cell, thus you generally want to have one cell in
between.

    Okay, so you are saying it is no big deal to do fast lookup in a 64K
    table, right ? I have not heard of Effnet, but that name has a
pretty
    embarrassing meaning in English.

    You have mentioned some interesting numbers, " You seem to be
ignoring
    the interframe spacing, the headers, ... .The average service time
for a
    64 byte packet by a Lucent WavePOINT-II AP is 918 usec
(microseconds) on
    the downlink and 190usec on the uplink.". Do you have a breakdown of
    these numbers?  From MN to AP, AP to Switch, Switch to whatever?
What do
    these
    64 byte packets contain?

64 bytes of payload

    As for 64K MN's sharing the same RF spectrum, I would not limit
myself
    to what is available today. You can in fact use directional/adaptive
    antennas etc. to do Spatial Division Multiplexing of radio waves.

Well if you are going to only consider the maximum possible case, then
why not consider entangled quantuum states, thus you have faster tha
speed of light communication across arbitrary distance? Of course you
may have to wait a year or more before this will be available in Radio
Shack.
Note that the look up time is no longer relevant, because you
communicate directly from the source to the destination and you don't
need any intervening network! 

Chip